Treatment of steel parts



United States Patent 3,411,958 TREATMENT OF STEEL PARTS Glenn T. Sink, San Pedro, and William H. Hyter, Los Angeles, Ca if., assignors, by mesne assignments, to McDonnell Douglas Corporation, Santa Monica, Calif., a corporation of Maryland No Drawing. Filed May 3, 1965, Ser. No. 452,913 17 Claims. (Cl. 1486.2)

ABSTRACT OF THE DISCLOSURE Method and composition for treating steel parts, and cadmium plated and zinc plated steel parts to prevent corrosion and especially hydrogen embrittlement thereof. The metal part to be treated is contacted with an aqueous acid solution consisting essentially of ammonium ion, nitrate ion, and hexavalent chromium ion and sufficient nitric or chromic acid to give a pH in the range from 0 to about 2.5. The inclusion of an acid stable wetting agent in the above solution is advantageous but optional.

This invention relates to the treatment of steel and plated steel parts to prevent brittle failure thereof, and is particularly concerned with procedure for the treatment of steel parts plated with a metal such a cadmium or zinc, and especially cadmium plated steel parts, to prevent hydrogen embrittlement of the steel, and to novel compositions employed in such treatment.

High strength steel, when subjected to a sustained tensile load, is susceptible to delayed brittle failure from the action of hydrogen. Such hydrogen can be produced in processing of the steel during its manufacture, during metal finishing operations such as pickling and plating, or such hydrogen can be produced as result of corrosion during service.

High strength steel parts are usually protected from corrosion by application of a metal plating to the steel surface, such as a cadmium or zinc plate, applied either electrolytically or by other means. For this purpose it has been found particularly useful in practice to apply a cadmium plate to the steel part. The metal plate, preferably cadmium, protects the steel base by corroding sacrificially. However, when the cadmium or other plate corrodes, hydrogen is released as one of the reaction products. Such hydrogen is released at the cathodic steel surface and can cause delayed brittle failure thereof, par ticularly if the steel has been heat treated to high strength. In present practice, the plated surface, eg the cadmium surface, is protected from corrosion by application thereto of a film or coating such as a chromate coating, e.g. as described in US. Patent 2,453,764, or by the application to the plated surface of a paint or grease.

It is accordingly one object of the invention to prevent corrosion and hydrogen embrittlement of steel parts, particularly plated steel parts.

Another object is to provide an improved procedure for preventing hydrogen embrittlement of steel parts, and of plated, particularly cadmium or zinc plated, steel parts, and especially steel parts plated with a thing coating of cadmium.

A still further object is to provide novel compositions for effective treatment of steel and of plated steel parts, to prevent corrosion or hydrogen embrittlement thereof in accordance with the invention procedure.

A still further object is to develop a novel procedure and chemical composition to prevent corrosion and/or hydrogen embrittlement of steel and plated steel, especially cadmium or zinc plated high strength steel, during processing and service.

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Other objects and advantages of the invention will appear hereinafter.

The above objects and advantages are achieved according to the invention by contacting bare steel parts or metal plated steel parts such as cadmium plated or zinc plated steel parts, with an aqueous acid solution containing ammonium, nitrate, and hexavalent chromium-containing ions and hydrogen ions, said solution havinga pH in the range from about 0 to about 2.5. It has been found that such chemical treating solution is non-corrosive and nonembrittling to bare and metal plated, e.g. cadmium or zinc plated, steel parts during chemical processing, and the film formed by such treatment increases the corrosion resistance and prevents corrosion-induced embrittlement of such parts. It has been found that treatment according to the invention is particularly advantageous for cadmium plated steel parts, and including steel parts plated with cadmium alloys, such as the well known cadmiumtitanium plating alloy, containing a small amount of titanium. Hence, the term cadmium plated steel parts is intended to include platings of pure cadmium and of alloys of cadmium on steel.

The treating solution can be formed by dissolving in water a mixture of suitable compounds which provide in solution the above-noted essential ions for treatment of the steel or metal plated, e.g. cadmium plated, steel parts. A preferred combination or mixture of compounds for this purpose comprises ammonium dichromate and ammonium nitrate. However, other combinations of compounds supplying the essential ammonium, nitrate and hexavalent chromium-containing ions in solution can be employed, for example, a mixture of alkali metal dichromate, e.g. sodium or potassium dichromate, and ammonium nitrate; a mixture of ammonium dichromate and sodium or potassium nitrate; and a mixture of ammonium dichromate and nitric acid. Also, the hexavalent chormium-containing ion can be supplied from chromic acid, that is, CrO and hence, a mixture of chromic acid and ammonium nitrate can be employed. In order to obtain the proper pH within the above noted range, preferably about 0 to about 1.5, and to supply the requisite hydrogen ion concentration, such pH adjustment is usually made by the addition of a suitable acid, preferably nitric or chromic acid. Particularly for treatment of zinc plated steel parts, it has been found advantageous to maintain the pH in the above noted preferred pH range, and most desirably a pH of about 0 is employed for this purpose.

The effective concentration of the above-noted essential ions of the aqueous treating solution can vary over a relatively wide range, from very dilute solutions substantially up to saturation of the ammonium, nitrate, and hexavalent chromium-containing ions. Thus, for example, an aqueous solution containing ammonium dichromate and ammonium nitrate each in concentration ranging from as low as 1 gram per liter up to approximately saturation produced useful results when adjusted to the proper pH as above noted. In general, it has been found that satisfactory results are obtained according to the invention employing, for example, from about 0.3 to about grams per liter of ammonium ion, from about 0.8 to about 200 grams per liter of nitrate ion, and hexavalent chromium-containing ion, e.g., chromate ion, in an amount equivalent to about 0.4 to about 200 grams per liter of hexavalent chromium. Preferably, the concentrations of such ions in terms of grams per liter, are about 0.6 to about 20 for the ammonium ion, about 1.5 to about 40 for the nitrate ion, and about 0.8 to about 20 for hexavalent chromium.

Thus, for example, useful treating solutions for preventing hydrogen embrittlement of steel or steel plated, e.g., cadmium or zinc plated, steel parts according to the invention, are those employing a combination of ammoni- 11111 dichromate and ammonium nitrate in varying or in approximately equal weight ratios to each other, representative solutions of this type being those which contain say from about 2 grams per liter up to about 50 grams per liter of each of these components. A particularly ading solutions which can be employed in the process of the invention, for increasing corrosion resistance and for preventing or minimizing hydrogen embrittlement of steel e.g. high strength steels, and particularly metal plated steels, especially cadmium plated steels.

TABLE I Compositions (grams per liter of solution) Wetting Agent pH HNO:

(71% couc.)

vantageous solution for purposes of the invention has been found to be one containing about 7 grams per liter of ammonium ion, about 25 grams per liter of nitrate ion, and hexavalent chromium-containing ion in an amount equivalent to about 8 grams per liter of hexavalent chromium, and having a pH in the above noted ranges, preferably ranging from about to about 1.5.

If desired, although not necessary, there can also be added to the aqueous treating solution a small amount of a wetting agent which is stable in such acid treating solutions at the pH thereof noted above. The employment of such optional wetting agents aids in providing thorough and uniform treatment and wetting of the surfaces of the parts, e.g., cadmium plated, steel parts being treated. Examples of suitable wetting agents include those marketed as Pluronic F 68, believed to be a reaction product of ethylene oxide and a condensation product of propylene oxide with propylene glycol, Igepal CO 630, believed to be alkyl phenoxy polyoxyethylene ethanol, Zero Mist, believed to be a sodium salt of perfiuoro heptanoic acid, Propaste 6708, believed to be fatty alcohol sulfate, chloroibenzenesulfonic acid, and Macrowet No. 2, a proprietary material. The amount of wetting agent employed can range from as little as a trace, e.g., a couple of drops per liter of solution, up to about or more grams per liter.

Treatment of the steel or metal plated steel parts, such as cadmium plated or zinc plated steel, is carried out in the above described treating solution at temperatures which can range from as low as about F. up to about 212 F. Preferably, the steel or metal plated steel parts according to the invention, are contacted with the treating solution while maintaining same at about ambient temperature of about 70 F. Time of treatment of the steel or metal plated, i.e. cadmium or zinc plated, steel parts in the treating solution can vary depending upon the concentration of the components of the solution, temperature of solution and thickness of coating desired to be deposited upon the steel or metal plated steel parts. Thus, time of treatment can vary from as little as about 5 seconds up to about 5 minutes, with the optimum treat- Macrowet No. 2, 0.4 cc Pluronic F 68, 5 g. Zero Mist, 4 g./l.

Propaste 6708, 1.5 g./l.

The following are examples of procedure for increasing corrosion resistance, and for preventing or minimizing hydrogen embrittlement of steel parts, and particularly metal plated steel parts such as cadmium and zinc plated steel parts, employing treating solutions of the type described above and illustrated in the table above.

Example 1 Panels of 4130 steel electroplated with cadmium were immersed in the respective aqueous treating solutions A, B, C, D and E noted above. These solutions were maintained at about ambient temperature during such treatment and the panels were immersed in such solutions for about 20 seconds.

The panels were then rinsed, dried and the coatings formed on the respective panels were inspected to determine which of the treating solutions produced the best conversion film based on color, consistency, coverage ability and wet strength. Based on these criteria, the best coatings were produced employing compositions A and B. However, the conversion coatings produced on those samples treated in solutions C, D and B were satisfactory.

Example 2 A first series of 4130 steel panels electroplated with cadmium were immersed in treating solution B above, at about ambient temperature for a period of 20 seconds. A second series of similar steel panels electroplated with cadmium were immersed for 20 seconds in a treating solution at ambient temperature, in the form of an aqueous solution of a proprietary conversion coating.

material for cadmium plated steel, marketed as Macrobronze #4, and not including the combination of the essential ammonium, nitrate and hexavalent chromiumcontaining ions, employing the recommended amount of 15 grams of such proprietary material per liter of solution.

Prior to treatment of both series of panels of the respective conversion coating compositions, the panels were first soaked and cleaned in a conventional cleaning solution and rinsed.

After treatment of the respective sets of panels in the invention composition and in the proprietary conversion coating material noted above, the panels were dried and placed in a salt spray cabinet for a total exposure time of 38 days, the panels being removed periodically for observation and returned.

A typical set of corrosion resistance results are noted in the table below.

TABLE II Composition B Proprietary Panel Salt Spray Composition Test, hrs.

Run 1 Run 2 Run 1 Run 2 0-no corrosion and a chromate film was visible.

1no corrosion but no chromate film was visible.

2-staining but no white corrosion products visible.

3\vhite corrosion products visible.

4chromate film removed and corrosion of base metal visible.

in the results noted in the table immediately above, it is seen that after 912 hours of salt spray treatment the cadmium plated steel panels treated in Composition B of the invention showed no corrosion, with the chromate film visible, whereas for those cadmium plated steel panels treated in the proprietary composition, the chromate film had been corroded and removed, and corrosion of the base metal was visible.

Example 3 Three samples of cadmium plated 1010 steel were provided. One of these samples remained untreated and had no conversion coating applied thereto and served as control. Another of the samples was treated in the invention Composition B above, the solution being maintained at ambient temperature, for 20 seconds, and the final sample was treated in the proprietary conversion coating composition Macrobronze #4 employing grams per liter of such composition, for seconds.

These samples or probes were each placed in the socket of a Lawrence Hydrogen Detection Gauge and immersed in a corrosive environment, in the form of an aqueous corrosion solution containing 10% by weight of sodium chloride and 10% by weight of sodium cyanide. The samples remained in the corrosion solution for a period of minutes.

The hydrogen evolved during corrosion of the samples was measured by standard procedure with the detection gauge, and the hydrogen peaks for each of the samples was thereby determined. The results of these tests are noted in the table below.

TABLE III Sample Chromate Hydrogen Treatment Peak 1 Control 2,875 Macrobronze #4 4, 999 3 Composition B 302 Example 4 Procedure similar to that of Example 3 was carried out except that each of the three samples of steel parts was only half cadmium plated, the other half of each of these parts being left as bare steel.

The results of these tests are noted in the table below:

TABLE IV Sample Chromate Hydrogen Treatment Peak 4 Control 1, 339 Macrobronze #4 899 6 Composition B"- 608 less hydrogen evolution during treatment in the corrosion solution as compared to the other four samples. From the results shown in the Tables III and IV above, these tests indicate that when subjected to a corrosive environment over a period of time, evolution of hydrogen from samples 1, 2, 4 and 5 would cause substantial hydrogen embrittlement on the base steel, whereas over the same time period, the substantially smaller amount of hydrogen evolution from samples 3 and 6 treated with the invention treating solution will cause substantially less or a minimum hydrogen embrittlement of the steel under the same corrosion conditions.

Example 5 Two zinc plated steel samples were provided. One of the samples was treated in Composition B of the invention, the solution being maintained at ambient temperature and at pH of 0, for 2 0 seconds. About 30 ml. of concentrated nitric acid was added per liter to Composition B, to obtain the above noted low pH. The other zinc plated steel sample was left in the as plated condition.

These two samples were each placed in the socket of a Lawrence Hydrogen Detection Gauge and immersed in a corrosive environment, in the nature of an aqueous corrosive solution containing 5% by weight of sodium chloride and 5% by weight of sodium cyanide. The samples remained in the corrosive solution for a period of 10 minutes.

The hydrogen evolution during corrosion of the samples in the latter solution was measured by standard procedure with the detection gauge, and the hydrogen peak for each of the samples was thereby determined. The results of these tests are noted in the table below.

TABLE V Sample Treatment Hydrogen Peak 1 Composition B 1.9 2 None 97.0

Example 6 Two bare steel samples having no plating thereon were provided. One of the samples was treated in the invention Composition C, the solution being maintained at ambient temperature and pH of 0.8, for seconds. The other sample was left in the untreated condition.

The bare steel sample treated with Composition C has substantially increased corrosion resistance as compared to the corrosion resistance of the other bare steel sample, when both samples are subjected to the same corrosive environment over the same period of time.

Although improved results are obtained by treatment of bare steel parts according to the invention, highly superior results are obtained by treatment of zinc plated and cadmium plated steel parts in accordance with the invention principles, particularly on cadmium plated steel parts.

From the foregoing, it is seen that the invention provides an improved procedure and novel compositions for treatment of steel parts, particularly metal plated, and especially cadmium or zinc plated, steel parts, so as to prevent or minimize hydrogen embrittlemen and delayed brittle failure of such steel parts, and substantially reduce corrosion.

It is known to treat ferrous metals in ammoniacal ammonium nitrate solutions containing free ammonia and in the presence of a small amount of a chromate.

However, the treatment solutions of the instant inven tion are of diiferent composition and are highly acidic, and are of particular value for treatment of cadmium plated and zinc plated steel.

While we have described particular embodiments of our invention for purposes of illustration, it will be understood that the invention is not to be taken as limited except by the scope of the appended claims.

We claim:

1. The method of treating a part selected fiom the group consisting of steel parts, and cadmium plated and zinc plated steel parts to prevent corrosion and hydrogen embrittlement, which comprises contacting said part with an aqueous acid solution consisting essentially of from about 0.3 to about 120 grams per liter of ammonium ion, from about 0.8 to about 200 grams per liter of nitrate ion, and hexavalent chromium-containing ion in an amount equivalent to about 0.4 to about 200 grams per liter of heXaValent chromium, and hydrogen ion supplied by an acid selected from the group consisting of nitric acid and chromic acid in a concentration such that said solution has a pH in the range from about to about 2.5.

2. The method of increasing the corrosion resistance and resistance to hydrogen embrittlement of a part selected from the group consisting of steel parts, and cadmium plated and zinc plated steel parts, which comprises contacting said parts with an aqueous acid solution consisting essentially of from about 0.3 to about 120 grams per liter of ammonium ion, from about 0.8 to about 200 grams per liter of nitrate ion, and hexavalent chromium-containing ion equivalent to about 0.4 to about 200 grams per liter of hexavalent chromium, hydrogen ion supplied by an acid selected from the group consisting of nitric acid and chromic acid in a concentration such that said solution has a pH in the range from 0 to about 2.5, and from a couple of drops to about grams per liter of a wetting agent which is stable in aqueous acid solutions having said pH.

3. The method of increasing the corrosion resistance andresistance to hydrogen embrittlement of a part selected from the group consisting of steel parts, and cadmium plated and zinc plated parts, which comprises contacting said part with an aqueous acid solution consisting essentially of from about 2 grams to about 50 grams per liter of ammonium dichromate and from about 2 grams to about 50 grams per liter of ammonium nitrate, said solution having a pH in the range from about 0 to about 2.5, and including a suflicient amount of an acid selected from the group consisting of nitric acid and chromic acid to produce said pH, and from a couple of drops to about 5 grams per liter of a wetting agent which is stable in aqueous acid solutions having said pH.

4. The method of increasing the corrosion resistance and resistance to hydrogen embrittlement of a part selected from the group consisting of steel parts, and cadmium plated and Zinc plated steel parts, which comprises contacting said part with an aqueous acid solution consisting essentially of about 2 to about 50 grams per liter of ammonium dichromate, and about 2 to about 50 grams per liter of ammonium nitrate, said solution having a pH in the range from about 0 to about 2.5, and including a sufiicient amount of an acid selected from the group consisting of nitric acid and chromic acid to produce said pH.

5. The method of preventing hydrogen embrittlement of a cadmium plated steel part, which comprises con tacting said part with an aqueous acid solution consisting essentially of about 2 to about 50 grams per liter of ammonium dichromate, and about 2 to about 50 grams per liter of ammonium nitrate, said solution having a pH from about 0 to about 1.5, and including a suflicient amount of an acid selected from the group consisting of nitric acid and chromic acid to produce said pH.

6. The method of preventing hydrogen embrittlement of a cadmium plated steel part, which comprises contacting said part with an aqueous acid solution consisting es sentially of about 20 grams per liter of ammonium dichromate and about 20 grams per liter of ammonium nitrate, and suflicient acid selected from the group consisting of nitric acid and chromic acid so that said solution has a pH in the range from about 0 to about 1.5.

7. The method of preventing hydrogen embrittlement of a zinc plated steel part, which comprises contacting said part with an aqueous acid solution consisting essentially of about 2 to about 50 grams per liter of ammonium dichromate, and about 2 to about 50 grams per liter of ammonium nitrate, said solution having a pH from about 0 to about 1.5, and including a sufiicient amount of an acid selected from the group consisting of nitric acid and chromic acid to produce said pH.

8. The method of increasing the corrosion resistance and resistance to hydrogen embrittlement of a steel part, which comprises contacting said part with an aqueous acid solution consisting essentially of about 2 to about 50 grams per liter of ammonium dichromate, and about 2 to about 50 grams per liter of ammonium nitrate, said solution having a pH from about 0 to about 1.5, and including a suflicient amount of an acid selected from the group consisting of nitric acid and chromic acid to produce said pH.

9. An aqueous solution for treating a metal part, which consists essentially of about 0.3 to about 120 grams per liter of ammonium ion, about 0.8 to about 200 grams per liter of nitrate ion, and an amount of hexavalent chromium-containing ion equivalent to about 0.8 to about 200 grams per liter of hexavalent chromium, and hydrogen ion supplied by an acid selected from the group consisting of nitric acid and chromic acid in a concentration such that the pH of the aqueous solution is in the range from about 0 to about 2.5.

10. An aqueous solution for treating a metal part,

which consists essentially of about 0.6 to about 20 grams per liter of ammonium ion, about 1.5 to about grams per liter of nitrate ion, and an amount of heXavalent chromium-containing ion equivalent to about 0.8 to about 20 grams per liter of hexavalent chromium, and hydrogen ion supplied by an acid selected from the group consisting of nitric acid and chromic acid in a concentration such that the pH of the aqueous solution is in the range from about 0 to about 2.5.

11. An aqueous solution for treating a part selected from the group consisting of steel parts, and cadmium plated and zinc plated steel parts, which consists essentially of about 2 to about grams per liter of ammonium dichromate and about 2 to about 50 grams per liter of ammonium nitrate, and suflicient acid selected from the group consisting of nitric acid and chromic acid so that said solution has a pH in the range from about 0 to about 2.5.

12. An aqueous solution for treating a part selected from the group consisting of steel parts, and cadmium plated and zinc plated steel parts, which consists essentially of about 2 to about 50 grams per liter of ammonium dichromate, about 2 to about 50 grams per liter of ammonium nitrate, suflicient acid selected from the group consisting of nitric acid and chromic acid so that said solution has a pH in the range from about 0 to about 2.5, and from a couple of drops to about 5 grams per liter of a wetting agent which is stable in aqueous solutions having said about pH.

13. An aqueous solution for treating a part selected from the group consisting of steel parts, and cadmium plated and Zinc plated steel parts, which consists essentially ofabout 7 grams per liter of ammonium ion, about 25 grams per liter of nitrate ion, and hexavalent chromium-containing ion in an amount equivalent to about 8 grams per liter of hexavalent chromium, the acidity of said solution being adjusted to a pH from about 0 to about 1.5 by the addition of an acid selected from the group consisting of nitric acid and chromic acid.

14. An aqueous solution for treating a part selected from the group consisting of steel parts, and cadmium plated and zinc plated steel parts, which consists essentially of about 20 grams perliter of ammonium dichromate and about 20 grams per liter of ammonium nitrate, said solution having a pH of about 0.8 and including a sufficient amount of an acid selected from the group consisting of nitric and chromic acid to produce said pH.

15. An aqueous solution for treating a part selected from the group consisting of steel parts, and cadmium plated and zinc plated steel parts, which consists essentially of about 7 grams per liter of ammonium ion, about 25 grams per liter of nitrate ion, and hexavalent chromium-containing ion in an amount equivalent to about 8 grams per liter of hexavalent chromium, the acidity of such solution being adjusted to a pH from about to about 1.5 by the addition of an acid selected from the group consisting of nitric acid and chromic acid, and from a couple of drops to about grams per liter of a wetting agent which is stable in aqueous solutions having said above pH.

16. An aqueous solution for treating a part selected from the group consisting of steel parts, and cadmium plated and zinc plated steel parts, which consists essentially of about 20 grams per liter of ammonium dichromate and about 20 grams per liter of ammonium nitrate, said solution having a pH of about 0.8, and including a suflicient amount of an acid selected from the group consisting of nitric acid and chromic acid to produce said pH, and from a couple of drops to about 5 grams per liter of a wetting agent which is stable in aqueous acid solution having said above pH.

17. An aqueous solution for treating a part selected from the g oup consisting of steel parts, and cadmium plaed and zinc plated steel parts, which consists essentially of a plurality of compounds which furnish in solution about 0.6 to about grams per liter of ammonium ion, about 1.5 to about grams per liter of nitrate ion, and an amount of hexavalent chromium-containing ion equivalent to about 0.8 to about 20 grams per liter of hexavalent chromium, and hydrogen ion supplied by an acid selected from the group consisting of nitric acid and chromic acid in a concentration such that the pH of the aqueous solution is in the range from about 0 to about 2.5.

References Cited UNITED STATES PATENTS 2,035,380 3/1936 Wilhelm 148-62 2,135,160 11/1938 Beekhuis 148-62 X 2,269,435 l/ 1942 Buzzard 148-62 2,393,663 1/1946 Thomas et al. 148-62 2,428,749 10/1947 De Long 148-62 2,625,468 1/1953 France et al. 148-62 X 2,796,369 6/1957 Chester 148-62 2,864,730 12/1958 Kinder et al. 148-627 X 2,961,358 11/1960 Heller 1486.27 X

RALPH S. KENDALL, Primary Examiner. 

